roughness creates an automatic "not perfectly smooth" appearance ranging from grainy to lumpy depending on your settings. It's advantage is you don't need to make a bumpmap for it. the disadvantage is that it is uniform, while a bumpmap lets yo create bumps in any shape you can draw. Roughness also slows rendering .
it used to be possible to export it in one of the poly formats and reimport the result. haven't tried it lately. However, current displacement maps do not depend on the density of the underlying mesh so an exported mesh may not resemble the rendered displacement.
This is for people working on collaborative projects off of a central server.
I'd have to see a specific example. My advice is to save frequently, in versions, so if you dont' like something you've done, you can go back to some point before you did it.